Flip chip bonding has emerged as one of the fastest growing technologies in packaging electronic components. Such technologies have developed in response to the demand for circuits which may operate at high speeds in high packing densities. Acceptable performance criteria may only be realized by appropriate selection of the substrate, interconnect mechanisms, flip chip design, and the bonding media (manufacturing reliable multi-chip modules).
Several methods may be used to attach a flip chip or die to a substrate. Solder is often used for silicon, aluminum nitride, alumina, or flexible substrates. Gold-to-gold thermocompression or ultrasonic bonding are mainly used for high power small devices. Standard conductive epoxy may also be used for flip chip bonding.
Among the issues which need to be considered when designing automated flip chip bonding mechanisms are placement accuracy, the types of flip chips and substrates, flip chip pickup and placement, substrate pickup and placement, throughput, and price.
Illustrative of previous approaches is U.S. Pat. No. 3,938,722 which discloses an apparatus for bonding flip chip devices onto mating conductive surfaces on a substrate utilizing ultrasonic energy. The bonding tool has a spherically shaped bonding surface which is caused by a pivoting mechanism to bond in a complex wobbling motion. Such approaches, however, may lead to relative lateral motion between the flip chip and the substrate which may jeopardize alignment.
U.S. Pat. No. 4,842,662 discloses a bonding approach wherein no gold globules or bumps are used in advance of the flip chip connection process. Such gold bumps are typically placed on the terminal pad of the flip chip and on the underside of the wire to be connected to the flip chip. The '662 disclosure, however, relates to single point bonding processes adapted for use with tape-automated-bonding (TAB) tape.
U.S. Pat. No. 5,341,979 discloses a thermosonic process for securing a semiconductor die to bonding pads on a substrate using multiple gold bumps. In such a process, heat is applied while ultrasonic energy is coupled to move the die in the horizontal, rather than vertical, plane. In contrast to this prior art, the process utilized in the present invention operates at room temperature, and the ultrasonic energy is delivered substantially isothermally in the form of vertical oscillations.